Tendons are fibrous connective tissues which attach muscles to bone; they also attach muscles to structures such as the eyeball and Ligaments are fibrous connective tissues which attache bone to bone and usually serves to hold structures together and keep them stable.

The Endomysium:

For a long time it was thought that a tendon and the fascia of its corresponding muscle were all one continuous piece, because both of them are fibroblastic tendon cells and because each fascicle in the muscle belly is identical to the fascicles in the corresponding tendon, but with the advent of the electron microscope, it became obvious that the muscle endomysium is a separate entity with its own connective tissue and is not the identical tissue as the tendon issuing from the muscle, even though they are the same type of cells.

The Golgi Tendon Organ (GTO):

The GTO attaches to the tendon at the point of union between the muscle
and tendon and it is attached to the endomysium, a layer of connective
tissue, composed mostly from reticular fibers, that ensheaths a muscle
fiber.

However, the distinction of the endomysial layers around the muscle
fibers and the perimysial layers around the Fascicles
which are not attached to the muscles, but forms a sheath around them,
continues in the tendon; therefore, tendons have the same logistical
separation into fascicles as do muscles, for the same logistical reasons.

Both the spindle and GTO are in parallel with the tendon; the muscle
spindle is attached to the side of the perimysium and the GTO is attached
to the side of the endomysial layer of the tendon; therefore, the GTO
is in parallel with the tendon that happens to be in series with the
muscle.

Tendon Reflex:

It is the tendon which is struck when checking tendon reflexes and striking
a tendon reflex point, on the knee, elbow or ankle, does not activate
a GTO; it is often mistakenly thought that the term Tendon Reflex refers
to activating the GTO, but GTOs actually inhibit rather than cause muscle
contraction; it is the muscle spindle bag fibers which cause muscle
contraction through the myotatic stretch reflex in response to stretching
within the muscle.

In the case of the knee tendon reflex, the GTO is located above the
knee, in the deflective portion at the end of the muscle belly; striking
there would produce only a local action from the deflection of the giving
fibers of the muscle, but striking just under the patella is striking
the less deflective tendon, which activates the entire muscle and because
we know that GTOs inhibit contraction, an erroneous assumption exists
in some camps that grinding away on the GTO will relax muscle in spasm,
but in fact, one cannot gnarl the GTO without activating the muscle
spindles, the stretch reflex.

Tendons and Ligaments:

Because tendons and ligaments are both connective tissue made from collagen fiber bundles, they are usually grouped together and thought of as closer relatives than tendons and muscles, but the muscle belly is not the total muscle; its tendons are a part of the muscle; in fact, the tendon is called the Stroma, or supporting framework, and the muscle belly is called the Parenchyma, or functional tissue of an organ, as distinguished from its connective or supporting tissue; together the stroma and the parenchyma make up the muscle tendon unit.

There are two main differences between tendons and ligaments; the first difference is that while both ligaments and tendons have bundles of parallel collagen fibers (collagen fibers are inherently elastic because they are parallel fibers of helical crystals, which look like a coiled spring), the fibers in ligaments are arranged in criss crossed layers, whereas the tendonís fibers remain in strictly parallel strands.

Ligaments are composed mainly of bundles of white fibrous tissue closely
interlaced with one another and present a white, shining, silvery aspect;
although ligaments are pliant and flexible, so as to allow freedom of
movement, they are nevertheless strong, tough, and not able to extend;
they are not involved in stretching and even though their main job is
to keep the joints together, ligaments do not become involved in maintaining
the integrity of movable joints unless the muscles are breached.

Elastic and Non-Elastic Ligaments:

Elasticity is not a desirable quality in ligaments because they act as backup to the muscle tendon unit; therefore, their inherent collagen elasticity is neutralized by the criss crossed layers of their fibers; however, white elastin between each layer of the ligament allows some movement between the layers for flexibility, change of motion, or direction, otherwise it would be an almost rigid structure.

However, having stated that, there are four examples of truly elastic ligaments in the human body, which are:

1 -
The Ligamentum Flavum, made from yellow elastic fibers rather than white elastic fibers, colouring the ligament yellow; it runs through the entire spinal column, all the way from top to bottom, because its job is to protect the spinal cord from the spinal column, it doesnít hold anything in place or stop any joints from dislocating, but is rather a soft, elastic curtain which gives with all the movements of the spinal column.

2 -
The Broad Ligament of the Uterus holds the uterus in place and of course has to stretch when the uterus expands, which is why itís elastic.

3 -
The Vocal Chords; we have two sets of vocal chords, vocal ligaments and vocal muscles; we get falsetto by relaxing the muscles so that nothing but the ligament is vibrating.

4 -
The Suspensory Ligaments in the Lens of the Eye; these have to be elastic, because when the eye muscles want to change the diameter of the lens, the ligaments have to stretch.

Tendon fiber bundles, on the other hand, are parallel and twisting rather
than criss crossed and overlapped, which allows them much more movement
than ligaments; the reason the tendon is twisting, by the way, is because
each one of its collagen fibers is twisting, so when these fibers are
combined, the tendon tends to twist, just like the DNA helix; when DNA
molecules are put together, one twists the next, and that in turn twists
the next one; in the same way, the inherent twisting of the collagen
fiber creates the twisting in the tendon.

Piezoelectricity:

The second difference between tendons and ligaments is that while ligaments
are totally passive structure, tendons, including retinaculae, are active
structure; this is because the tendonís helical crystals are piezoelectric,
like the crystal in a digital watch, or inkjet printer, where a miniscule
amount of energy applied to the crystal makes it pulse or vibrate.

Piezoelectricity has to do with electricity or electric polarity produced
in certain non conducting crystals when subjected to pressure or strain;
piezoelectricity turns rapidly pulsing electrical currents into rapidly
pulsing mechanical action; the Piezoelectric crystals expand and contract
when injected with electricity and they also generate electricity when
mechanically distorted; the muscle therapist is mainly interested in
the fact that when electricity (innervation) is introduced into the
piezoelectric helical coil spring of the collagen tendon fiber, it tenses,
or stiffens, rather than contracts.

Where does that Electricity/Innervation come from?

The motor nerves that innervate muscle fibers give off co-laterals,
little parallel sidetrack nerves, some of which go to the muscle spindles
and some to tendons of the muscles theyíre innervating; tendons must
stiffen at the same time the muscles contract, or they would stretch
out and counteract the contracting action of the muscle belly; there
would be no shortening of the muscle tendon unit, so again, tendons
are active, while ligaments are passive.

Some articles state that tendons, when over-stretched, undergo permanent
elongation and loss of elasticity; if this were true, we would become
permanently disjointed; what really happens is that the muscle becomes
hypertonic because more and more fibers are contracting continually,
which creates added stress on the tendons, which then become extra-fibrotic.

Remember, each collagen fiber is a coiled spring; say there are four
coiled springs which are operating very well within their limits of
stretch under a certain stress, but if more stress were added, it would
overstretch the springs until additional coils were also added; the
tendons have the ability to call for more springs, because the extra
piezoelectric voltage given off stimulates the fibroblasts to produce
more fibers, thus spreading the stress of the permanently contracting
(hypertonic) muscle over a larger number of coils, until the tendons
are back within the range of their allowed limits.

Although the tendon is still elastic, the extra fibrosity makes it harder
to move and stretch, it takes more force to make it happen; for that
reason, when muscle tone increases, the stretch reflex decreases; the
muscle no longer needs to resist force and protect itself through dynamic
contraction as much because it canít stretch as much as it used to.

However, even when oneís tendons are fibrotic, the stretch reflex mechanism
is activated in repeated or intense stretching, driving the muscle crazy
and even someone with an extremely shortened muscle belly can temporarily
extend the tendon, which is why ballet theaters have a barre in the
back of the stage; as dancers dance and use their muscles, the co-lateral
nerves running to their tendons tell the tendons to stiffen.

Once offstage, the dancers stretch out their tendons at the barre, but
as soon as they dance again, the tendons shorten up; this stretching/stiffening
of the tendons does nothing except possibly thicken them with more coils,
but a dancerís shortened muscle bellies, which have lost their range
of motion, are also stretched at the barre, driving them into more contraction
(hypertonic spasm); thatís why the derriŤres of ballet dancers tend
to bulge out, the gluteal muscles are incredibly spastic.

Muscle fibers twitch on and off in a fraction of a second, but tendons,
once stiffened, take longer to let go; because of this and the fact
that they donít provide much movement, tendons cannot be used in place
of muscles.

Damaged Ligaments:

If ligaments do not heal within several weeks, they may remain chronically
stretched, torn, or strained; many people do not realize how severe
or prolonged ligament pain can be; they assume that soft tissue will
heal or that it canít be that bad; while ligament pain may be confined
to the injury site, it can also refer pain to distant body parts through
a portion of the autonomic nervous system called the sympathetic nerves.

The region that a ligament refers pain to is called a sclerotome and
Ligament pain can mimic nerve impingement, cause sensations of numbness
and be the source of arthritis pain; it can be chronic, persistent,
achy, burning, and weather sensitive.

The primary function of ligament is to connect bone to bone and if a
ligament is stretched, or torn, then too much movement between the bones
may occur; this extra movement is perceived as a popping, clicking,
catching, or feeling of weakness between the bones; the muscles respond
by going into spasm, in an effort to tighten the area down; many people
will try to stretch tight muscles, or strengthen weak ones, in an effort
to reduce the pain; they become discouraged, however, when this approach
only offers temporary relief.

Ligament Treatment:

In order to obtain lasting relief, the underlying ligament injury must
be treated first; a physical exam by a doctor experienced in ligament
injuries and testing using Musculoskeletal Ultrasound or MRI, can confirm
the diagnosis; if treating ligament pain does not provide pain relief,
then an electrodiagnostic study to rule out sensory or motor nerve injury
is often useful; since ligament pain will not respond to treatment if
a sensory motor nerve is involved, just like a muscle wonít respond
if there is ligament injury, in chronic cases it makes sense to check
for nerve involvement before trying to treat either the muscle or ligament
further.

When addressing the ligament portion of pain, exercise, which only strengthens
muscle, should not be forgotten; fortunately, strengthening exercises
can take up to 20 per cent of the pressure off a joint and therefore
remove some of the stress occurring at a weakened ligament; physical
therapy to stretch whatís tight and re-educate whatís inhibited is also
important; medications to reduce spasm, pain and inflammation are often
used as well; in most cases, a special injection is needed to actually
repair, or re-grow the injured ligament.

The medication injected is not steroid, which weakens ligament, but
rather a combination of xylocaine with sodium morruhate, dextrose, or
other special agents that stimulate the bodyís own natural wound healing
response; just like a scab on skin, the new ligament grows to replace
what is missing; if repeated once every two weeks or so, the ligament
will become 40 per cent thicker than it was before treatment; in extreme
cases surgery may be needed.

Since the ligaments actually thicken, this technique is often referred
to as Prolotherapy; it can be very helpful in relieving pain, weakness,
and sensations of numbness for many conditions, including neck and back
pain, sports injuries, and arthritis; moreover, since the body actually
repairs the injury site, in the absence of other problems there is no
reason to worry about re-occurrence.